The Use of Free Radical Probes in the Study of Mechanisms of Enzyme Inactivation

Some inorganic radical-anions, which have very strong absorption spectra, have some oxidative reaction specificity with amino acids. Combined pulse radiolysis and inactivation studies on the reactions of these radicals with several enzymes lead to identification of amino acid residues essential to enzymic activity. Data are reviewed for the enzymes, lysozyme, ribonuclease, trypsin, α-chymotrypsin, papain and carboxypeptidase. The reducing radical, CO₂^?, is more selective than the hydrated electron in its reactions with enzymes and proteins. Results from pulse radiolysis studies in electron-transfer and other reactions involving CO₂^? are compared with results from inactivation studies with lysozyme and ribonuclease.